Tumor treatment methods include, as one method for treating a tumor, radiation treatments of irradiating an affected site with a radiation beam. In the radiation treatments, it is desirable to effectively irradiate the affected site with the radiation beam while minimizing an irradiated dose of the radiation beam (a dose) applied to a patient.
To achieve this, there have been used multileaf collimators for regulating a field of irradiation which is a radiation region/a radiation shape of a radiation beam.
Such a multileaf collimator includes a plurality of leaves in the shape of thin plates. The leaves are, in a frame, arranged side by side and spaced from each other along a plate thickness direction of the leaves. Further, each of the leaves is configured to be independently movable by means of a drive mechanism, and therefore allowed to be individually advanced into or retreated from the radiation region of the radiation beam. When the leaves are positioned in the radiation region, the radiation beam is screened by the leaves, to thereby regulate the field of irradiation. That is, regulating the field of irradiation can achieve formation of a field irradiated with the radiation beam adjusted for each patient.
In the multileaf collimator, it is necessary that the radiation beam should be prevented from leaking through a gap between leaves adjacent to each other. Patent Literature 1 discloses a structure in which a protrusion is provided to a first surface of a leaf and a groove is provided to a second surface of the leaf. In this structure, the protrusion on a first one of mutually adjacent leaves is inserted into the groove in a second one of the mutually adjacent leaves. This structure can function to prevent leakage of the radiation beam through a space between the mutually adjacent leaves.